1. Field of the Invention
The present invention relates to an apparatus for processing substrate and method of processing the same and, more particularly, to an apparatus for processing a coating film, a heating apparatus for a coating film, heating method using the heating apparatus and resist pattern formation method relating to a lithography process.
2. Description of the Related Art
The manufacture of a semiconductor device uses a resist pattern in formation of an element region, processing of electrode wiring, and the like. This resist pattern is generally formed as follows. After a resist coating film is formed on a semiconductor wafer, heating processing called pre-bake is performed. In pre-bake, a solvent in the resist is volatilized. Then, a predetermined pattern is transferred to the resist film by exposure.
Along with micropatterning of semiconductor elements, high resolution is required in lithography. To meet this demand, the wavelength of exposure light used is being shortened. In photolithography, a KrF excimer laser (wavelength: 248 nm) has widely been used as an exposure light source.
Along with a shortened wavelength of exposure light, a photoresist called a chemically amplified resist as a photosensitive resin (photoresist) material for transferring a pattern has been devised and put into practical use. The chemically amplified resist contains an acid generator which generates an acid by exposure. The acid generated by exposure decomposes (positive type) or crosslinks (negative type) a resin. The property that the solubility to a developing solution changes is utilized in the subsequent developing step.
The chemically amplified resist is excellent in resolution but is sensitive to the environment. The chemically amplified resist reacts with a basic material in air, and the acid is deactivated to degrade the pattern shape or resolution. To prevent this degradation, the environment is controlled. To control the environment, a chemical filter or the like is generally attached in a coater/developer for coating/developing a resist.
Most of chemically amplified resists require a heating processing step called PEB (Post Exposure Bake) after the exposure step. PEB diffuses an acid generated in the exposure step. After the PEB processing step, the chemically amplified resist is exposed to a developing solution to form a desired resist pattern.
The chemically amplified resist is known to disappear due to evaporation of the acid in PEB processing, in addition to deactivation of the acid. Several conventional methods of reducing disappearance of the resist due to evaporation of the acid in PEB processing have been proposed. For example, the temperature of pre-bake performed to volatilize the solvent after resist coating is set higher than a general one, and the PEB temperature is set lower than a general one, thereby reducing evaporation of the acid (“Effect of acid evaporation in Chemically Amplified resists on insoluble layer formation” Journal of Photopolymer Science and Technology Vol. 8, Number 4 (1995), pp. 561-570: to be referred to as reference 1 hereinafter). As another method, evaporation of the acid is reduced by executing PEB processing at a pressure higher than general atmospheric pressure (Jpn. Pat. KOKAI Publication No. 11-38644: to be referred to as reference 2 hereinafter).
According to reference 1, the evaporation amount of the acid in PEB can be reduced. However, pre-bake processing and PEB processing are done under conditions greatly different from optimal temperature conditions (normal conditions). The original resist performance such as the margin of exposure dose (amount) of focus cannot be fully exploited.
PEB processing requires a heating apparatus capable of preventing gas or particles produced upon heating from being deposited inside a chamber and serving as a particle generation source, as shown in FIG. 65. This heating apparatus comprises an air inlet port 6501 formed in one side surface of a chamber 6500, and a discharge port 6502 formed in the facing other side surface. A gas 6504 is flowed between the air inlet port 6501 and air outlet port 6502 along the upper surface of a semiconductor wafer W on a hot plate 6503, thereby generating an air stream within the chamber.
As shown in FIG. 66, acids evaporated in PEB is carried downstream by the air stream , as indicated by arrows in FIG. 66, and adsorbed to the wafer again. The acid concentration on the resist surface differs between a chip at the uppermost stream of the air stream and a chip at the lowermost stream. Thus, the width of resist pattern varies within the wafer plane after developing processing.
In reference 2, evaporation of the acid can be reduced, but no measure is adopted for adsorption of an evaporated acid. Since the evaporated acid is adsorbed to a semiconductor wafer again, it is difficult to prevent variations in resist width within the wafer plane after developing processing.